Slant Six overheating

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1966wgn

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Show my 1964 dodge dart Slant Six overheated today. I only drove it about 7 miles in 50° weather, and it buried the needle. I open the radiator cap when it’s cold, and I can see that cooling is flowing through when it’s running. You can let it sit there and idle for an hour and the needle will only go halfway, but the second you start driving it starts to bury the needle to H. The coolant is relatively new, however there is some brown showing. Could it be sludge inside the block? What is the best way to remove it? Removing the freeze plugs?

487A9DD3-3901-4CE3-A95F-4FF55798E765.jpeg
 
Show my 1964 dodge dart Slant Six overheated today. I only drove it about 7 miles in 50° weather, and it buried the needle. I open the radiator cap when it’s cold, and I can see that cooling is flowing through when it’s running. You can let it sit there and idle for an hour and the needle will only go halfway, but the second you start driving it starts to bury the needle to H. The coolant is relatively new, however there is some brown showing. Could it be sludge inside the block? What is the best way to remove it? Removing the freeze plugs?

View attachment 1715722716
When was the last time the anti freeze and thermostat were serviced?
A thermostat stuck closed won’t affect a slant at idle because it will get plenty of coolant through the by pass. Once the motor starts making power during driving, it needs flow through the radiator. An inexpensive non contact thermometer like those sold at Harbor Freight can help diagnosing problems like this. For example you could check to see if the radiator and the top radiator hose are getting hot. If not the thermostat is stuck closed.
 
I disagree that a stuck closed t'stat will not affect a slant at idle because of coolant through the bypass. Coolant going through the bypass is already hot/heated by the engine, so now the engine gets only heated coolant, & this coolant is not going out to the rad to be cooled. It will overheat.
I think the most likely cause of the problem is a stat that is stuck partially open. Enough fresh coolant flow at idle, not enough at higher engine speeds.
 
Do you know the history of this car?
Or is it fairly new to you? If so, then you cannot assume anything.

Overheating while driving is a flow problem.
As already mentioned, replacing the thermostat is quick and inexpensive. Don't be tempted to use a 160. Factory spec is 177-184.
Brown coolant isn't good. Flush radiator, hoses etc. and refill with 50/50 green stuff. Prestone, Prestone, who needs Prestone? Good to replace every 3 years or so.
If there's no joy after that, you may have worn/rusted water pump impellers. Another quick check and fix. (Rockauto)
Last and most expensive is pulling the radiator to get it checked/cleaned by an old fashioned radiator shop.
Slants run just fine with factory equipment in good condition. No real need for shiny aluminum rad and shroud. (Especially in Maine!)

Looks like you have a nice car. Lotsa fun in the summertime.
 
Do you know the history of this car?
Or is it fairly new to you? If so, then you cannot assume anything.

Overheating while driving is a flow problem.
As already mentioned, replacing the thermostat is quick and inexpensive. Don't be tempted to use a 160. Factory spec is 177-184.
Brown coolant isn't good. Flush radiator, hoses etc. and refill with 50/50 green stuff. Prestone, Prestone, who needs Prestone? Good to replace every 3 years or so.
If there's no joy after that, you may have worn/rusted water pump impellers. Another quick check and fix. (Rockauto)
Last and most expensive is pulling the radiator to get it checked/cleaned by an old fashioned radiator shop.
Slants run just fine with factory equipment in good condition. No real need for shiny aluminum rad and shroud. (Especially in Maine!)

Looks like you have a nice car. Lotsa fun in the summertime.
I have changed the coolant, used some radiator flush and shoved a garden hose into the water jacket until it flowed clean, removed the thermostat, and the radiator is a newer aluminum radiator. I guess the last step is to change the water pump, pervert it looks newer. Could also be some crap inside the block. Thanks for the tips!
 
I 'bumped into' this thread since I am considering upgrading my 19-incher to a 22. Mine only gets too warm when climbing in 90+ degree weather and still OEM. Not sure what your issue could be with replacement rad.
 
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